DESCRIPTION (Applicant's abstract): The broad, long-term objective of this research is to understand how higher-order concepts are learned. The proposal expands upon findings regarding concept learning and list memory in rhesus monkeys and pigeons. The experiments for each species are virtually identical, permitting an excellent cross species comparative investigation. The first set of experiments explores parameters associated with the underlying mechanisms of learning and transfer of same-different (SD) discriminations. An SD judgment requires a subject to respond "same" when two items are identical and "different" when two items are different from each other. The experiments directly test the hypothesis that increased observing responses (i.e., number of pecks or touches to a stimulus) lead to relational learning by inducing the elemental analysis of a visual stimulus (Wright, 1997). The role of the observing response is further tested in the second set of experiments examining list memory. These list memory experiments use the more complex serial-probe-recognition (SPR) task in which a sequentially presented list of items is followed by a probe item. The specific aims of this new research are to (1) compare the strategies and mechanisms underlying SD discriminations between two different species, (2) evaluate the role of the observing response on concept learning, (3) evaluate the interaction of observing responses and set size on concept learning, (4) evaluate how basic concepts transfer to more complex problems, and (5) evaluate the role of the observing response on list memory.